1. Field of the Invention
The present invention relates to a developing apparatus used in image forming apparatus such as copiers and printers, and to a developer regulating member for regulating a developer, used in the developing apparatus.
2. Related Background Art
In the image forming apparatus of the electrophotographic method) the developing apparatus visualizes an electrostatic latent image formed on an image carrying member, in the form of a toner image.
As one type of such developing apparatus, a variety of dry-type monocomponent developing apparatuses were proposed and are under practical use. It is, however, not easy to form a thin layer of toner as a monocomponent developer on a developer carrying member in either one of the developing apparatus.
An improvement is demanded in resolution, visibility, and the like of image nowadays, and it is essential to develop a method and apparatus for forming the thin layer of toner. Some measures were proposed as to such method and apparatus.
For example, as described in Japanese Laid-open Patent Application No. 54-43038, there is a developing apparatus in which a rubber or metal elastic blade is set in contact with a developing sleeve of the developer carrying member and in which the toner is regulated as being passed through the contact portion between the elastic blade and the developing sleeve, whereby the thin layer of toner is formed on the developing sleeve and friction in the contact portion causes sufficient triboelectricity on the toner.
For regulating non-magnetic toner by the above elastic blade, a separate toner supply member for supplying the toner onto the developing sleeve becomes necessary. The reason is that in the case of magnetic toner the toner can be supplied onto the developing sleeve by magnetism of a magnet in the developing sleeve, whereas in the case of the non-magnetic toner the toner cannot be supplied by magnetism.
Thus, the developing apparatus shown in FIG. 4 was proposed in Japanese Laid-open Patent Application No. 58-116559. In this conventional developing apparatus proposed, an elastic roller 27 of fur brush structure in contact with the developing sleeve 26 is disposed at an upstream position in the rotating direction of the developing sleeve 26 with respect to the elastic blade 25 in a developer container 24 containing the nonmagnetic toner 23 as a monocomponent developer, and the elastic roller 27 scrapes the residual toner 23 remaining on the developing sleeve 26 without being consumed for development and also supplies new toner 23 onto the developing sleeve 26.
The above-stated structure enabled the thin film of non-magnetic toner 23 to be formed well on the developing sleeve 26 and thus enabled an electrostatic latent image to be developed well on the image carrying member.
However, demands for a further improvement in quality of image and for a further reduction in consumption energy induced the need for use of toner with smaller particle sizes and with lower melting point. In repeating the developing operation with a such toner many times, the following problems arose.
(1) When a thin metal plate of SUS, phosphor bronze, or the like is used as the elastic blade, longitudinal contact is likely to become nonuniform because of its too high hardness, so that coating unevenness of toner tends to occur on the developing sleeve. Further, the too high hardness causes excessive force to be applied locally on the toner and poor releasability of surface causes the toner to be fused on the surface of elastic blade in contact with the developing sleeve after repetition of the developing operation. This results in coating unevenness of toner or stripes on the developing sleeve, thus in turn resulting in poor quality of image.
(2) If the elastic blade is a plate of conventional urethane rubber, silicone rubber, or the like used singly or one formed by bonding such rubber onto a metal thin plate in order to achieve stable contact throughout long-term operation, the problem of (1) will be avoided, but triboelectrification capability to the toner will become insufficient, making triboelectricity insufficient on the toner. This will result in fog as a problem of image, and in the worst case it raises the problem that the toner is scattered from the developing sleeve to contaminate the inside of image forming apparatus.
Thus, the elastic blade itself needs to be made of a material with high triboelectrification capability. A material having high electron accepting property is selected for toner of positive polarity, while a material having high electron donating property is selected for toner of negative polarity.
There were various proposals on use of materials in which a charge control material of high electron donating property was added in a base material of silicone rubber, urethane rubber, or the like, especially for the negative-polarity toner among the above, but they were not sufficient yet in terms of the triboelectricity given to the toner. They were not successful yet in preventing occurrence of a foggy image especially under high-humidity circumstances.
In order to prevent this occurrence of a foggy image, materials of further higher electron donating property are effective, and for example, polyamide resins such as nylon are used. Since the polyamide resins do not have elasticity, it is of course impossible to use them in a plate shape singly. It is conceivable that they may be used in the form of a coating on a thin metal plate as a supporting layer for regulating pressure or in the form of a plate of resin bonded thereto.
Employment of this structure was able to prevent the occurrence of a foggy image in the initial state of developing operation, but on the other hand it raised coating unevenness of toner on the developing sleeve in the initial state and occurrence of fusion of toner to the surface of elastic blade after repetition of the developing operation, as in the above case of using the metal thin plate singly. A cause of this is of course that excessive force is exerted on the toner passing the elastic blade because of the too high hardness of polyamide resin. For decreasing the hardness, the elastic blade was thus constructed in such structure that, for example, urethane rubber was bonded as an elastic layer onto a metal thin plate and that a thin coating of polyamide resin was formed as a charge giving layer on the surface of urethane rubber. This structure improved the stability of toner coating on the sleeve, as compared with the structure in which the polyamide resin was directly formed on the thin metal film, but after repetition of the developing operation under high-temperature circumstances, this structure also resulted in fusion of toner at a high-hardness portion, because the hardness of polyamide resin itself was high in the surface layer. Thus, this structure was not preferable.
Accordingly, properties desired for the elastic blade are the excellent charge giving property to the toner and possession of appropriate hardness to allow the toner to pass in an appropriate layer thickness through the contact portion without exerting the excessive force thereon in the contact portion. The above conventional materials and structures failed to meet these properties sufficiently and thus failed to prevent fog and fusion of toner.
It was proposed in Japanese Patent Application No. 7-155511 that the elastic blade was made of a polyamide elastomer containing a polyamide component of good triboelectrification capability to the negative toner and a polyether component having elasticity.
It was, however, found that simply using this material was not enough to prevent the fog and fusion of toner and it was necessary to further define a proper range of hardness of the polyamide elastomer in use in order to draw the full performance.
With too low hardnesses, the desired triboelectrification capability cannot be attained, so that the fog occurs especially under high-humidity circumstances. This is because low-hardness polyamide elastomers include low contents of the polyamide component in the formulation thereof and therefore the electron donating property of the elastic blade to the negative toner is too low.
Too high hardnesses will cause coating unevenness due to fusion of toner, because the excessive force is exerted on the toner passing the elastic blade, as being the case with the polyamide resin of the conventional example described above.